I have a question regarding CFX Pre. I would like to set a monitor in a following way:

[*]Monitor volume (inside fluid domain) which is defined as Iso-volume at value (this can be done in POST - no clue if possible in PRE).[*]For instance I want to measure volume of air inside fluid domain, which has Temperature = 350K and I would like to monitor that in solver manager during simmulation

The function 'volumeInt' referenced in parameter 'Expression Value' in object '/FLOW:Flow Analysis 1/OUTPUT CONTROL/MONITOR OBJECTS/MONITOR POINT:Cloud Size' has an invalid argument, 'AirVFInTempRange'. Only arguments that consist of a single recognised variable name are supported by the solver.

First of all - I used a volume integral over the volume fraction. This gives the total volume. Your post #3 does a volume integral of the molar fraction which is a different thing, and will not give volume.

Second - The error message is clear, if cannot find the variable it is naming. Sometimes CEL gets the order of expressions mixed up as it is trying to evaluate the AirVFInTempRange expression after the volumeInt expression and this leads to an error as the volumeInt expression has undefined variables. Try putting the entire expression on one expression: